The retinal pigment epithelium (RPE) plays a critical role in the maintenance of normal photoreceptor functions and has been implicated in several visual disorders, including macular degenerations and dystrophies. The investigator has cloned and characterized the first known RPE-specific human gene, RPE65, and has shown that mutations in this gene are responsible for certain forms of autosomal recessive childhood-onset severe retinal dystrophy (arCSRD), a finding supported by reports of RPE65 defects in Leber's congenital amaurosis. A research program has been developed to study the function of RPE65 in the normal biology of the retina and in the disease state, based on the view that RPE65 is necessary for the isomerase activity involved in the conversion of vitamin A to 11-cis retinal. Four specific aims have been identified for the proposed funding period. (1) Recombinant protein-protein interactions and enzyme activity will be studied in cultured cells transfected with RPE65 expression constructs in order to distinguish between the two prevailing hypotheses about the specific role of RPE65 in RPE retinoid metabolism. (2) Site-directed mutagenesis will be used with assays of expression and protein function to elucidate the role of RPE65 mutations in the pathogenesis of arCSRD to test the hypothesis that disease-associated mutations in RPE65 result in functional null alleles that disrupt the 11-cis retinal biosynthetic pathway. This aim will include further characterization of mutations present in patient populations. (3) Because preliminary information indicates that RPE65 is down-regulated by a variety of factors that are known to be related to aging and disease processes, and because decreased levels of RPE65 are implicated in retinal degeneration, the mechanisms involved in this down-regulation will be investigated, as well as the effects of aging and other physiological conditions on RPE65 expression. (4) Effects of the RPE65 mutation in a large animal model of arCSRD will be characterized in assays of the biochemistry and enzymology of retinoid metabolism, to test the hypothesis that defects resulting from RPE65 mutations will be amenable to retinal replacement therapy. The long-term goals of this project are to elucidate the mechanisms by which RPE65 defects contribute to retinal degeneration, and to lay the groundwork for the development of therapeutic approaches to the disease.